1. Field of the Invention
The present invention refers to a method for the positioning of components with reference to a workpiece, comprising the steps of removing the component from a magazine or a storage bin or from one certain magazine or storage bin from a group of magazines or bins, transporting the component to the workpiece and putting the component onto or into the workpiece exactly at a preselected position. The invention further refers to an apparatus suitable to perform the above mentioned method, the apparatus comprising at least one component magazine or storage bin or a magazine or storage bin group, at least a component transportation device provided with a pick-up and retaining member for the components and at least one workpiece receiving and retaining station adapted to receive a workpiece, said component transportation device being displaceable between the magazine or storage bins and the workpiece receiving station.
A preferred field of an application of the present invention may be seen in the manufacturing of electronic circuitry, particularly in the placing of electronic components on a supporting element. As supporting elements. e.g. printed circuit boards, ceramic substrates for hybrid circuitries or similar workpieces may be considered. Such supporting elements include a flat conductor carrier board consisting of epoxy resin, ceramic material or the like, the surface thereof being equipped, on the one hand, with a certain pattern of electrically conductive traces and, on the other hand, with a plurality of connecting points provided to receive discrete electrical or electronical components like e.g. resistors, capacitors, transistors etc. Particularly in view of the small dimensions and the tight arrangement found at hybrid circuitries, it is of paramount importance that the components to be placed onto the surface of the supporting element be situated with the highest possible precision at a desired position, before they are soldered to the connecting points and conductive traces provided on the surface of the supporting element.
2. Prior Art
In the interest to realize an economical manufacturing process of such electronic circuitry, automated to the highest possible degree, it is known to use automatic assembly machines, which are controlled by a suitable program and which automatically pick-up selected components from a magazine or from a certain magazine of a magazine group, transport these components to the circuit board and finally place the components on the surface of the circuit board at an exactly predetermined location. With the knowledge of the prior art available up to now it is possible to control the transportation device, which brings the component from the magazine to the workpiece, with the required high precision. On the other side, it must be mentioned that the position of the components in the magazine can not be guaranteed with the required high precision so that the position of a component picked up by the transportation device may be deviated with reference to a theoretical, nominal position axis. With other words, this means, that a component retained by the pick-up and retaining member of the transportation device may be shifted and/or tilted with regard to the desired nominal position.
In order to correct this not-presumable position deviation, one has proposed hitherto to provide the pick-up means of the transportation device with centering elements in order to shift an unexactly gripped component to the desired nominal position with reference to the theoretical positioning axis, i.e. to shift the component mechanically until the symmetry axis thereof coincides with the theoretical positioning axis of the transportation device. Such an apparatus is disclosed e.g. in U.S. Pat. No. 4,135,630, showing an arrangement for the centering of electronic components which have been removed from a magazine and which have to be placed on a circuit board. It is thereby assumed that the components to be placed on the circuit board have been eccentrically gripped and therefore can not be placed correctly, i.e. not in the required nominal position on the surface of the circuit board. In order to avoid such incorrect placing, the mentioned Patent proposes to use a centering device, with the help of which the components removed from the magazine may be exactly centered with regard to a theoretical, nominal positioning axis of the transporting device.
Basically this method and this apparatus, respectively, work satisfactory, but mechanically complicated and expensive elements are required in order to grip and mechanically shift the electronic components picked-up from the magazine, which usually have quite small dimensions, in an attempt to bring them into the theoretically required nominal position. The design and manufacturing of such a centering device, which must be made to meet very high precision standards, is therfore very delicate and expensive.
Furthermore, attention must be paid to the fact that one has to consider a remarkable wear which impairs the working precision of the centering device, and further, that under certain circumstances a destruction or damage of the components may occur. A further disadvantage of the known arrangement lies in the fact that the mass to be accelerated and deaccelerated is quite high; in the interest of a short cadence in placing a plurality of components onto a circuit board, the driving means for the transportation device, which also has to include the mentioned centering device, must be made very powerful.
Finally, it is a disadvantage of the known arrangement that usually a plurality of differently sized centering devices must be available which can be removably connected to the pick-up member on the transportation device in order to center components of different sizes. Besides the undersired timeconsuming job of changing such centering device, the comparatively high expenditure and investment for the stock of different centering devices must also be considered.